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Myocardial perfusion is the process by which blood is supplied to the heart muscle from the left and right coronary arteries. Exploring the structure of microvascular trees in a detailed way will provide a deeper understanding of the mechanisms that rule myocardial perfusion.

Researchers from Western University, London, investigated arteriolar trees, the pre-capillary levels of the microvasculature, using a combination of imaging techniques, experimental methodologies, and theoretical constructs.

Micro-CT was used as the vascular imaging method. This avenue provided an accurate description of the intramyocardial arterioles, consistent with the micro scale of these vessels, which range in root diameter from several hundreds to less than 20micrometers. From micro-CT scans of left ventricular walls of porcine hearts, the group extracted microvascular trees by tracing all the branches and sub-branches using a “connect” feature within Analyze software.

After measuring the diameter of each vessel segment from the myocardial specimens, the investigators were able to infer the flow rate, derived from a power law relationship, within each tree.

Results from this study provided further information regarding the parameters present in the equation, in particular, the power law exponent. The values of the index increased at branching stages of the arterial tree closer to the capillary level, indicating, therefore, that the index increases in the direction of small diameters. On the other hand, the researchers observed a decrease in the levels of shear stress affecting the inner wall of the vessels as the diameters decreased. The team collected information about shear stress, the mechanism through which the endothelium cells – cells that line the interior surface of blood vessels – respond to variations in flow rate.  In fact, the level and distribution of shear stress is likely to play a crucial role in the efficiency and regulation of myocardial perfusion.

This study was able to estimate, for the first time, the trend of the power law index using microvascular imaging of arteriolar trees. Future studies will focus on how this value and, by implication, the level or distribution of shear stress, contribute to the performance and regulation of myocardial perfusion.

Tags: Heart Disease